telemetry: Add Windows throw-site stack trace capture

Summary: Adds Windows throw-site stack trace capture. On Windows, C++ exceptions are implemented as Structured Exception Handling (SEH) events with the [magic code 0xE06D7363](https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/specific-exceptions). A [Vectored Exception Handler](https://learn.microsoft.com/en-us/windows/win32/debug/vectored-exception-handling) filters for this code to detect C++ throws and captures the stack trace via the shared onThrow() infrastructure. Completes cross-platform support — Linux, macOS, and Windows all now capture throw-site stack traces.

Reviewed By: vilatto

Differential Revision: D102222780

fbshipit-source-id: a3ac9b3c54acad5ec3c778d6a7030a1532591e46

Author: Chandhana Solainathan

eden/fs/telemetry/ThrowTraceCapture.cpp

@@ -12,14 +12,13 @@
 #ifdef __APPLE__
 #include <dlfcn.h>
 #endif
+#ifdef _WIN32
+#include <windows.h>
+#endif
 
 #include "eden/fs/rust/backtrace_ffi/src/lib.rs.h"
 
-#if defined(__linux__) || defined(__APPLE__)
-
 namespace {
-// Common: onThrow() captures a raw backtrace via Rust FFI.
-// Re-entrancy is handled by the Rust CapturingGuard in capture_backtrace().
 void onThrow() {
   constexpr size_t kMaxStackDepth = 64;
   facebook::eden::capture_backtrace(kMaxStackDepth);
@@ -68,9 +67,51 @@ __cxa_throw(void* thrownException, void* type, void (*destructor)(void*)) {
   __builtin_unreachable();
 }
 
-#endif // platform hooks
+#elif defined(_WIN32)
+// Windows: Vectored Exception Handler catches C++ exceptions (SEH 0xE06D7363).
+
+constexpr DWORD kCppExceptionCode = 0xE06D7363;
+
+LONG WINAPI cppExceptionHandler(PEXCEPTION_POINTERS info) {
+  if (info && info->ExceptionRecord &&
+      info->ExceptionRecord->ExceptionCode == kCppExceptionCode) {
+    onThrow();
+  }
+  return EXCEPTION_CONTINUE_SEARCH;
+}
+
+// AddVectoredExceptionHandler first parameter: CALL_FIRST (1) registers our
+// handler at the front of the VEH list so it runs before other handlers,
+// ensuring we capture the stack trace before the exception is modified.
+// See:
+// https://learn.microsoft.com/en-us/windows/win32/api/errhandlingapi/nf-errhandlingapi-addvectoredexceptionhandler
+#define CALL_FIRST 1
+
+struct VehRegistrar {
+  PVOID handle_ = nullptr;
+  VehRegistrar(const VehRegistrar&) = delete;
+  VehRegistrar& operator=(const VehRegistrar&) = delete;
+  VehRegistrar(VehRegistrar&&) = delete;
+  VehRegistrar& operator=(VehRegistrar&&) = delete;
+
+  VehRegistrar() {
+    handle_ = AddVectoredExceptionHandler(CALL_FIRST, cppExceptionHandler);
+    if (!handle_) {
+      fprintf(
+          stderr,
+          "Failed to register VEH for throw-site stack trace capture\n");
+    }
+  }
+  ~VehRegistrar() {
+    if (handle_) {
+      RemoveVectoredExceptionHandler(handle_);
+    }
+  }
+};
+
+static VehRegistrar vehRegistrar;
 
-#endif // defined(__linux__) || defined(__APPLE__)
+#endif // platform hooks
 
 namespace facebook::eden {
 

eden/fs/telemetry/ThrowTraceCapture.h

@@ -23,6 +23,7 @@ namespace facebook::eden {
  * Platform-specific hooks:
  *   Linux:   __wrap___cxa_throw (via --wrap linker flag)
  *   macOS:   __cxa_throw override (via dlsym RTLD_NEXT)
+ *   Windows: Vectored Exception Handler (SEH code 0xE06D7363)
  */
 std::optional<std::string> getThrowSiteStackTrace();
 

eden/fs/telemetry/test/EdenErrorInfoBuilderTest.cpp

@@ -37,13 +37,17 @@ TEST(EdenErrorInfoTest, InitializeFuseEdenErrorInfoWithException) {
     EXPECT_NE(
         info.exceptionType.value().find("runtime_error"), std::string::npos);
     ASSERT_TRUE(info.stackTrace.has_value());
+    EXPECT_NE(info.stackTrace->find("Stack trace:"), std::string::npos)
+        << "Stack trace should contain raw trace section, got: "
+        << *info.stackTrace;
+#ifndef _WIN32
+    // Windows without PDB debug info can't resolve file paths or function names
     EXPECT_NE(
         info.stackTrace->find("EdenErrorInfoBuilderTest.cpp"),
         std::string::npos)
         << "Stack trace should contain source file, got: " << *info.stackTrace;
-#ifdef __linux__
-    EXPECT_NE(info.stackTrace->find("Stack trace:"), std::string::npos)
-        << "Stack trace should contain raw trace section, got: "
+    EXPECT_NE(info.stackTrace->find("throwRuntimeError"), std::string::npos)
+        << "Stack trace should contain the throwing function, got: "
         << *info.stackTrace;
 #endif
   }

eden/fs/telemetry/test/ThrowTraceCaptureTest.cpp

@@ -14,7 +14,6 @@
 
 using namespace facebook::eden;
 
-#ifdef __linux__
 namespace {
 
 [[noreturn]] FOLLY_NOINLINE void innerThrowingFunc() {
@@ -26,23 +25,21 @@ namespace {
 }
 
 } // namespace
-#endif
 
 TEST(ThrowTraceCaptureTest, CapturesThrowSiteStackTrace) {
-#ifndef __linux__
-  GTEST_SKIP() << "Stack trace capture not yet implemented on this platform";
-#else
   try {
     outerThrowingFunc();
   } catch (const std::exception&) {
     auto trace = getThrowSiteStackTrace();
     ASSERT_TRUE(trace.has_value()) << "Stack trace capture is broken";
+#ifndef _WIN32
+    // Windows without PDB debug info can't resolve function names
     EXPECT_NE(trace->find("innerThrowingFunc"), std::string::npos)
         << "Expected throw-site function in trace, got: " << *trace;
     EXPECT_NE(trace->find("outerThrowingFunc"), std::string::npos)
         << "Expected caller function in trace, got: " << *trace;
-  }
 #endif
+  }
 }
 
 TEST(ThrowTraceCaptureTest, ReturnsNulloptOutsideCatchBlock) {